1. Field of the Invention
The present invention relates to a reproducing method for reproducing data by scanning slant tracks with a helical scan technique, and a reproducing apparatus reproducing data using such a reproducing method.
2. Description of Related Art
Conventionally, as a data recording/reproduction method using a magnetic tape as a storage medium, a helical scan technique is extensively employed. In the helical scan technique, a magnetic tape 100 is wrapped at a slant angle around a rotary head drum 101 as shown in, for example, FIG. 10. Under this condition, the tape 100 is moved so that the head drum 101 rotates in the direction of the arrow, whereby a head scans at the slant angle with respect to the tape running direction. In this way, tracks are formed on the tape 100 by recording data at slant angles with respect to the tape running direction, or data is reproduced from such tracks, as shown in FIG. 11.
Furthermore, the above-mentioned helical scan technique adopts so-called azimuth recording. In azimuth recording, a pair of heads is used with their gaps slanted at different azimuth angles A and B, respectively, to alternately form on the magnetic tape 100 a track TkA depicting a recording pattern at the azimuth angle A and a track TkB depicting a recording pattern at the azimuth angle B, as shown in FIG. 11.
To reproduce data from a track recorded by such azimuth recording as mentioned above, a reproducing head 102A corresponding to the track TkA is used, and a reproducing head 102B is used for the track TkB recorded at the azimuth angle B as shown in FIG. 12. In this way, signals produced from adjacent tracks can be suppressed from affecting each other as noise owing to the azimuth effect, whereby a higher density recording can be implemented.
As one data reproducing technique in the helical scan technology, a tracking servo system is widely known in the art, in which each of the thus formed tracks is read by single scanning performed by a reproducing head. As shown in, for example, FIG. 13, the tracking servo system controls a reproducing head 102 to keep the head constantly right above a track Tk so that all the data recorded on the track Tk will be read by causing the single head 102 to scan only once.
Thus, in the tracking servo system, error information is gathered, for example, by comparing a block-based scanning time with a pre-defined reference value in each track Tk, and the scanning position of the reproducing head 102 is controlled based on the error information to maintain the so-called “just tracking state” (Japanese Unexamined Patent Application Publication No. H9-245394).
As another reproducing technique in the helical scan technology, a non-tracking (NT) system is known in the art. In the NT system, recorded data is scanned during reproduction at a track twice of that of the recording period. Reproduced signals are obtained twice on the average per track, and the better one is used for the data reproduction.
FIG. 14 conceptually shows the relationship between recorded tracks and reproducing heads in a NT system. Note that a description is given only of reproduction of azimuth tracks A in FIG. 14, and a description of azimuth tracks B will be omitted. Here, the tracking servo system as a reproducing technique would use reproducing heads 103 and 105 to scan tracks TkA-1 and TkA-2 to reproduce data, respectively. By contrast, the NT system, which scans data during reproduction at a track twice of that of during recording period, would cause a reproducing head 104 to intervene for scanning between the scanning operations performed by the reproducing heads 103 and 105.
In an example shown in FIG. 14, the track TkA-1 is scanned by the heads 103 and 104, and both heads provide effective reproduced signals for the track TkA-1. In this case, however, a comparison between the heads 103 and 104 indicates that the head 103 overhangs the track TkA-1 wider and, in addition, is less likely to near the track TkA-2 next to the adjacent track of the track TkA-1. Therefore, the reproducing head 103 will provide a more satisfactory reproduced signal. And only a correctly read portion of the thus reproduced signal is re-arranged to provide stream data. Such an NT system requires neither accurate tracking servo nor accurate scanning angle with respect to tracks, thus making the system free from mechanical tolerances, for example.